Apparatus for advancing conveyors of mining machines in underground excavations

ABSTRACT

A double-acting hydraulic cylinder and piston unit whose cylinder is connected to a mobile mine roof support and whose piston rod is attached to and can push a material evacuating conveyor stepwise toward the mine face in an underground excavation. The piston rod is hollow and its interior communicates with an annular chamber in front of the piston. A plunger in the piston rod is movable between a front stop and a rear stop and is biased against the rear stop by a helical spring. A distributor valve is provided to admit pressurized liquid into a second chamber behind the piston so that the piston moves forwardly and expels fluid from the annular chamber into the piston rod with the result that the plunger moves against the front stop and prevents further forward movement of the piston rod. The valve is then reset to allow the outflow of fluid from the annular chamber while the fluid in the second chamber remains entrapped whereby the plunger returns against the rear stop under the action of the spring. The piston again moves the piston rod and the conveyor forwardly in response to renewed admission of fluid into the second chamber while the annular chamber is sealed against escape of fluid. The piston can complete a stroke of maximum length if the second chamber receives fluid while the valve allows fluid to escape from the annular chamber. The cylinder is moved forwardly to pull the mine roof support toward the mine face by admitting pressurized fluid into the annular chamber while the valve allows fluid to escape from the second chamber.

United States Patent [191 Roenspies et al.

[ Dec. 31, 1974 APPARATUS FOR ADVANCING CONVEYORS OF MINING MACHINES IN UNDERGROUND EXCAVATIONS [75] Inventors: Hans-Christian Roenspies,

Bochum-Langendreer; Manfred Vogt, Herne, both of Germany [73] Assignee: Kloeckner-Werke AG, Duisburg,

Germany 22 Filed: Apr. 12,1973

21 Appl. No.: 350,469

[30] Foreign Application Priority Data Apr. 26, 1972 Germany 2220452 [52] US. Cl 61/45 D, 91/418, 91/421, 91/469, 92/8, 92/l3.4, 92/13 [51] Int. Cl... E2ld ll/00, Fl5b 13/04, F15b 15/24 Primary Examinerlrwin C. Cohen Attorney, Agent, or FirmMichael S. Striker [57] ABSTRACT A double-acting hydraulic cylinder and piston unit whose cylinder is connected to a mobile mine roof support and whose piston rod is attached to and can push a material evacuating conveyor stepwise toward the mine face in an underground excavation. The piston rod is hollow and its interior communicates with an annular chamber in front of the piston. A plunger in the piston rod is movable between a front stop and a rear stop and is biased against the rear stop by a helical spring. A distributor valve is provided to admit pressurized liquid into a second chamber behind the piston so that the piston moves forwardly and expels fluid from the annular chamber into the piston rod with the result that the plunger moves against the front stop and prevents further forward movement of the piston rod. The valve is then reset to allow the outflow of fluid from the annular chamber while the fluid in the second chamber remains entrapped whereby the plunger returns against the rear stop under the action of the spring. The piston again moves the piston rod and the conveyor forwardly in response to renewed admission of fluid into the second chamber while the annular chamber is sealed against escape of fluid.

The piston can complete a stroke of maximum length if the second chamber receives fluid while the valve allows fluid to escape from the annular chamber. The cylinder is moved forwardly to pull the mine roof support toward the mine face by admitting pressurized fluid into the annular chamber while the valve allows fluid to escape from the second chamber.

21 Claims, 4 Drawing Figures SL857. 24s

PATENTEU 15:3 1 1974 SHEET 2 OF 3 1 17 .v/// r llllfflllllflllllll FIG. 2

PATENTEDBEB3 1 IBM 7 3.857. 246

sum 3 0F 3 APPARATUS FOR ADVANCING CONVEYORS OF MINING MACHINES IN UNDERGROUND EXCAVATIONS BACKGROUND OF THE INVENTION The present invention relates to apparatus for moving parts of mining machines or analogous bulky and heavy structures, and more particularly to improvements in apparatus which can be used to displace material evacuating conveyors and mine roof supports in underground excavations. Still more particularly, the invention relates to improvements in fluid-operated (preferably hydraulic) motors which are utilized in underground excavations to push m'aterial evacuating conveyors and material removing tools toward the mine face as well as to pull mobile mine roof supports toward the mine face.

It is already known to utilize in underground excavations an elongated material evacuating conveyor which rests on the mine floor in front of the mine face and serves to evacuate material which is being removed by one or more tools. The material removing means may comprise one or more planes which are moved lengthwise of the mine face and must be shifted forwardly at certain intervals so as to be capable of removing successive layers of material (e. g., coal) from the mine face. As a rule, the means for shifting the conveyor and the material removing means toward the mine face comprises a battery of hydraulic motors in the form of double-acting cylinder and piston assemblies each of which is mounted on a discrete mine roof support and is coupled to the conveyor. It is often important to insure that the material removing tool or tools will travel along a straight path, i.e., to shift the conveyor forwardly by increments of predetermined length. Since the conveyor normally carries or embodies guide means for the material removing tools, it should be advanced in such a way that it provides for the tools an elongated straight path to thus contribute toward a higher output of the mining machine as well as to reduce the wear on the moving parts of the conveyor. lt was found that the wear on the relatively movable parts of the conveyor (which is normally assembled ofa large number of sections articulately connected to each other to be capable of following the outline of an uneven mine floor) is much less pronounced and the useful life of such parts is much longer if the conveyor extends along a straight line. Moreover, the shifting of the material evacuating conveyor by steps of identical length facilitates the transport of mine roof supports toward the mine face. In many instances, the hydraulic motors which push the conveyor forward are integrated into or operatively connected with the mine roof supports so that the supports serve as anchors for the hydraulic motors during pushing of the conveyor toward the mine face and that the conveyor thereupon serves as an anchor for the hydraulic motors during pulling of the mine roof supports toward the mine face. The mine roof supports of presently preferred design comprise one or more sole plates which rest on the mine floor, one or more caps which can engage the roof in an underground excavation, and one or more hydraulic pit props which can be expanded to push the caps against the roof and the sole plates against the floor or contracted to allow for transport of the mine roof support toward the mine face.

It was already proposed to construct the hydraulic motors for pushing of the material evacuating conveyor in such a way that the motors can perform shorter or longer strokes, thus enabling the operators to advance the conveyor through distances of desired length. To this end, the conventional hydraulic motors are associated with auxiliary aggregates which can admit into the doubleacting cylinders metered quantities of a hydraulic fluid. Each aggregate comprises a metering cylinder which can accumulate a selected quantity of fluid prior to introduction of such fluid into the cylinder of the respective hydraulic motor. The initial and maintenance cost of auxiliary aggregates is high and they occoupy substantial amounts of space, normally in the crowded region between the conveyor and the mine roof supports. Also, the auxiliary aggregates are prone to malfunction because they are mounted close to the mine floor which is covered with dust and fragments of removed material and/or waste. The auxiliary aggregates are not readily accessible so that their malfunctioning can cause lengthy interruptions in the mining operation.

SUMMARY OF THE INVENTlON An object of the invention is to provide a novel and improved hydraulic motor which can be used in a machine for removal of material in underground excavations to push the material evacuating conveyor and the material removing equipment toward the mine face and/or to pull one or more mobile mine roof supports toward the mine face.

Another object of the invention is to provide an apparatus which embodies the improved hydraulic motor and can be used to push the materialevacuating c0nveyor and the material removing equipment toward the mine face.

A further object of the invention is to provide the hydraulic motor with novel and improved means for selecting its strokes so that the motor can advance a conveyor through distances of selected length without resorting to bulky, expensive and unreliable auxiliary aggregates.

An additional object of the invention is to provide a hydraulic motor which can be installed in existing mining machinery for transport of the material evacuating conveyor and/or mine roof supports toward the mine face.

Another object of the invention is to provide a hydraulic motor of the above outlined character with a built-in stroke limiting and selecting system which is cheaper than the aforementioned auxiliary aggregates and contributes little to the cost, bulk and sensitivity of the motor.

The invention is embodied in an apparatus for displacing or shifting conveyors or the like, particularly for pushing a material evacuating'conveyor and one or more material removing tools toward the mine face in an underground evacation. The apparatus comprises an anchor (preferably a so-called walking mine roof support which can be immobilized in an underground excavation by pressing its cap or caps against the roof and by pressing its sole plate or plates against the floor in anexcavation, one or more valves, a source of pressurized fluid, and a fluid-operated motor which includes an elongated doubleacting cylinder having a closed end (which can be connected to the anchor or to the conveyor), a piston which is reciprocable in and defines with the cylinder a first chamber adjacent to the closed end of the cylinder, a hollow piston rod which is provided with a fluid-filled axially extending compartment and is connected to the piston so that one of its ends extends from the cylinder in a direction away from the closed end of the cylinder and is connec table to the conveyor or to the anchor, a fluid-filled second chamber which is defined by the piston rod with the piston and cylinder and is separated from the first chamber by the piston so that the volume of the second chamber decreases when the volume of the first chamber in- I creases and vice versa, a plunger which is movable axially in the compartment of the piston rod between a first stop against which the plunger abuts when it is nearest to the piston and a second stop which is preferably adjustable in the axial direction of the piston rod, a helical spring or other suitable biasing means for yieldably urging the plunger against the first stop, and one or more ports or analogous passages provided in the piston rod or in the piston to establish communication between the second chamber and the compartrrient in the piston rod.

The valve means preferably comprises a multi-way distributor valve which is actuatable (either by hand or automatically) to connect the source of pressurized fluid with the first chamber to thus increase the distance between the closed end of the cylinder and the end of the piston rod so that the conveyor and the material removing means move away from the anchor, either by movement of the cylinder relative to the piston and piston rod or vice versa. As the volume of the first chamber increases, the volume of the second chamber decreases whereby the fluid flows from the second chamber into the compartment (by way of the aforementioned port or ports) and displaces the plunger which moves from the first stop toward and against the second stop to thus interrupt the admission of fluid into the first chamber.

The distributor valve is further actuatable to thereupon seal the first chamber against escape of fluid therefrom and to connect the second chamber (or the compartment of the piston rod) with a tank or with the atmosphere (depending upon whether the pressurized fluid is a liquid or a gas) so that the biasing means is free to return the plunger against the first stop.

The piston is movable in the cylinder through a predetermined maximum distance exceeding preferably several times the distance which the piston must cover in order to transfer from the second chamber into the compartment enough fluid to move the plunger from the first stop against the second stop. Thus, the piston can cover the maximum distance in at least two stages the second of which takes place in response to renewed admission'of pressurized fluid into the first chamber upon completed return movement of the plunger against the first stop and while the second chamber and the compartment are sealed to prevent the outflow of entrapped fluid.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved apparatus itself, however, both as to its construction and its mode of operation, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of certain specific embodiments with reference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic horizontal sectional view of a mining machine which serves to remove material from the mine face in an underground excavation and comprises a battery of apparatus for moving the material evacuating conveyor toward the mine face;

FIG. 2 is an enlarged axial sectional view of the hydraulic motor of one of the apparatus shown in FIG. 1;

FIG. 3 is a fragmentary axial sectional view of a modified motor; and

FIG. 4 is a similar fragmentary axial sectional view of a further motor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The mining machine'of FIG. 1 comprises a conveyor 2 which extends along the mine floor close to the mine face 1 in an underground excavation. The conveyor 2 comprises an elongated scraper chain 3 and a composite frame including elongated guide means 4 for a material removing tool 5 (here shown as a plane) which travels back and forth lengthwise of the conveyor 2 and removes material (e.g., coal) from the mine face 1. Such material is thereupon evacuated by the conveyor 2. The means for moving the tool 5 lengthwise of the conveyor 2 includes one or more chains 6 or analogous drive means.

The conveyor 2 can be advanced sideways toward the mine face 1 by'a battery of displacing apparatus including so-called walking mine roof supports 8 which are adjacent to the filled end of the underground excavation and each of which includes one or more hydraulic pit props 8b of variable length which support one or more mine roof engaging caps (not shown) to prevent collapse of the roof in the area behind the conveyor 2. FIG. I merely shows the sole plates 8a and the lower portions of props 8b in each of the four illustrated mine roof supports 8. The supports 8 further serve as anchors for discrete hydraulic motors 7 which form part of the respective displacing apparatus and can push the conveyor 2 forwardly in stepwise fashion through distances of selected length as well as pull the respective supports 8 forwardlytoward the mine face 1. The arrangement is such that, when the tool 5 has removed a layer of material from the mine face 1 and it becomes necessary to push the conveyor 2 with the guide means 4, tool 5 and drive means 6 toward the mine face, the props 8b are extended so that the respective sole plates 8a bear against the mine floor and the respective caps bear against the mine roof. This insures that the mine roof supports 8 are fixedly held against any movement toward or away from the mine face. In the next step, the motors 7 are operated to push the conveyor 2 forwardly toward the mine face whereby the supports 8 act not unlike anchors or retainers to enable the motors 7 to move the conveyor 2 forwardly. When the conveyor 2 reaches the desired position at a selected distance from the mine face 1, the props 8b are caused to contract so that the caps of the mine roof supports 8 are disengaged from the mine roof 8 and the sole plates 8a merely rest on the mine floor by gravity. The motors 7 are thereupon operated to pull the respective mine roof supports 8 toward the mine face 1 before the props 8b are expanded again to prevent a collapse of the roof behind the conveyor 2. The space behind the supports 8 is then filled with waste material and the tool 5 is ready to begin with removal of material from the mine face. It is clear that the tool 5 can be set in motion as soon as the conveyor 2 has been shifted forwardly to move closer to the mine face so that the cutting edge or edges of the tool can bite into the material of the mine face.

The hydraulic motors 7 receive pressurized hydraulic fluid (e.g., oil) from a suitable source including a pump (not shown) which can be located at a substantial distance from the excavation, and a supply conduit 9 which connects the pump with the motors 7. A return conduit 10 is provided to deliver spent fluid back to the source, e.g., into the tank (not shown) for the pump. The conduits 9 and 10 extend lengthwise of the chain 3 behind the conveyor 2 and contain spaced-apart distributor valves 11, one for each of the mine roof supports 8. Each distributor valve 11 is connected with the respective hydraulic motor 7 by two flexible conduits or hoses 12, 13. The conduits 9 and 10 extend transversely of the hydraulic motors 7 and are adjacent to these ends of the motors which are articulately connected with the conveyor 2.

FIG. 2 illustrates portions of the conduits 9, 10, a hydrualic motor 7, the corresponding distributor valve 11, and the associated flexible hoses l2, 13. The hydraulic motor 7 is a cylinder and piston assembly of the doubleacting type and comprises an elongated cylinder 14 the rear end of which is closed by a head 15 which is articulately connected to the corresponding mine roof support 8 (not shown in FIG. 2). The cylinder 14 receives a working piston 16 which is rigid with an elongated tubular piston rod 17 for a reciprocable stroke-limited plunger 18. Theplunger 18 is coupled to the piston 16 or to a portion of the piston rod 17 in the region of the piston 16 by a helical spring 19 which tends to pull the plunger toward the head 15 and nor mally maintains the plunger in abutment with a first stop 20 here shown as an internal shoulder of the piston rod 17.

The piston 16 is provided with circumferential grooves for two ring-shaped sealing elements 21 which prevent leakage of fluid between a first cylinder chamber 26 at the rear of the piston 16 and an annular second cylinder chamber 24 between the cylinder 14 and the piston rod 17. The plunger 18 is also provided with circumferential grooves for ring-shaped sealing elements 22 which prevent escape of hydraulic fluid from the compartment 17a of the piston rod 17. A further sealing structure 23 is provided in the open front end of the cylinder 14 to prevent escape of fluid from the annular chamber 24.

The hose 13 connects the valve 11 with the annular chamber 24 immediately behind the sealing structure 23. The chamber 24 is in communication with the compartment 17a of the piston rod 17 by way of one or more radial ports or passages 25 machined into the piston rod immediately in front of piston 16. The chamber 26 of the cylinder 14 is connected with the valve 11 by way of the hose 12.

The front end of the piston rod 17 extends forwardly beyond the cylinder 14 and is provided with several transverse bores 27 on reception of a second abutment or stop in the form of a bolt 28 which can be held against axial movement in the selected bore 27 by a nut 28a. The bores 27 are staggered with respect to each other, as considered in the axial direction of the piston rod 17, and the exposed portion of the piston rod is protected by a sleeve 29 having bores which register with the bores 27.

The foremost end of the piston rod 17 carries a head 30 which is articulately connected to the conveyor 2.

The operation:

The head 15 at the closed rear end of the cylinder 14 shown in FIG. 2 is assumed to be connected to the respective mine roof support 8 and the head 30 at the front end of the piston rod 17 is assumed to be connected to the conveyor 2. It is further assumed that the conduit 9 contains pressurized fluid and that the conduit 10 serves to return fluid from the hydraulic motor 7 to the tank.

In the setting which is shown in FIG. 2, the distributor valve 11 connects the supply conduit 9 with the cylinder chamber 26 by way of the hose l2 and simultaneously seals the hose 13 from the return conduit 10. The pressurized fluid flows into the chamber 26 in front of the head 15 and causes the piston 16 to move forwardly toward the sealing structure 23. Thus, the volume of the chamber 26 increases and the volume of the annular chamber 24 decreases with the result that the fluid (which cannot escape by way of the hose 13) flows through the port or ports 25 and into the cocmpartment 17a of the piston rod 17 to push the plunger 18 forwardly toward the second stop 28. Thus, the spring 19 stores energy. The forward movement of the piston 16 is terminated when the plunger 18 reaches the stop 28 because the latter prevents admission of further fluid into the compartment 17a of the piston rod 17. It will be noted that the length of the forward stroke of the piston 16 can be selected at will by the simple expedient of inserting the second stop 28 into a selected bore 27 in the front end portion of the piston rod 17. During movement away from the head.l5, the piston 16 causes the piston rod 17 to push the head 30 forwardly and to thus advance the conveyor 2 toward the mine face 1. As mentioned before, the mine roof supports 8 cause their caps and sole plates to respectively engage the mine roof and the mine floor while the chambers 26 of the cylinders 14 receive pressurized fluid so that the mine roof supports 8 constitute anchors and prevent the heads 15 from moving rearwardly during admission of pressurized fluid into the cylinder chambers 26.

Prior to carrying out a further working stroke, the hydraulic motor 7 of FIG. 2 must expel some fluid from the annular chamber 24 and/or from the compartment 17a of the piston rod 17. To this end, the distributor valve 11 is adjusted in such a way that the hose 13 communicates with the return conduit 10. This enables the spring 19 in the piston rod 17 to contract and to expel fluid from the annular chamber 24 into the return conduit 10 by way of the hose 13 because the plunger 18 moves rearwardly and away from the second stop 28 to thereby cause fluid to flow from the compartment 17a of the piston rod 17, through the port or ports 25 and into the annular chamber 24. The plunger 18 terminates its rearward movement toward the head 15 when it reaches and engages the shoulder 20 in the piston rod 17. During retraction of the plunger 18 from engagement with the second stop 28 into engagement with the shoulder 20, the valve 11 seals the supply conduit 9 from the hose 12 so that the chamber 26 behind the piston 16 cannot discharge any fluid. 1

The next working stroke can begin as soon as the plunger 18 reengages the shoulder 20. The valve 11 is then reset to seal the hose 13 from the return conduit 10 and to connect the supply conduit 9 with the hose 12 so that the chamber 26 receives additional fluid and the piston 16 moves further toward'the sealing structure 23 with the result that the fluid flows from annular chamber 24 into the compartment 17a of the piston rod 17 and the plunger 18 advances toward and into engagement with the second stop 28. The same procedure can be repeated again and again until the piston 16 reaches or approaches the sealing structure 23. During each of the just discussed working strokes of the piston 16 (from close proximity to the head toward close proximity to the sealing structure 23), the respective mine roof support 8 continues to engage the mine roof as well as the mine floor to hold the head 15 against movement away from the mine face 1.

If the piston 16 is to be returned to the position shown in FIG. 2, the props 8b are shortened so as to disengage the respective support 8 from the mine roof and to reduce the pressure between the sole plates 8a and the mine floor. The valve 11 is then reset to connect the hose 12 with the return conduit 10 and to simultaneously admit pressurized fluid into the annular chamber 24 (from the supply conduit 9 and by way of the hose 13). The fluid which flows into the chamber 24 then pushes the piston 16 rearwardly and the piston 16 expels fluid from the chamber 26. Actually, the piston 16 remains at a standstill because the admission of pressurized fluid into the annular chamber 24 results in forward movement of the cylinder 14 whose head 15 thereby entrains the respective mine roof support 8 toward the mine face 1. During admission of pressurized fluid into the annular chamber 24, the fluid which flows through the port or ports 25 into the compartment 17a pushes the plunger 18 toward and into engagement with the second stop 28 and the plunger 18 thereupon remains in such foremost position during forward movement of the cylinder 14 so that the head 15 moves close to the piston 16. It is clear that the plunger 18 will not change its axial position if the admission of pressurized fluid into the chamber 24 (via valve 11 and hose 13) takes place upon completion of the last working stroke when the plunger 18 already engages the second stop 28. a

If the operators wish to move the piston 16 all the way from the head 15 to the sealing structure 23 in a single stroke, the valve 11 is set to connect the: hose 13 with the return conduit 10 and to simultaneously connect the supply conduit 9 with the hose 12. The pressurized fluid which flows into the chamber 26 then pushes the piston 16 forwardly toward the sealing structure 23 and the piston 16 expels fluid from the annular chamber 24 by way of the hose 13, valve 11 and return conduit 10. The spring 19 is preferably strong enough to maintain the plunger 18 in engagement with the shoulder 20 to reduce the fluid-receiving volume of the compartment 17a in the piston rod 17 to a minimum when the valve 11 permits fluid to flow from the chamber 24 into the return line 10 during admission of pressurized fluid into the chamber 26.

It will be seen that the valve 11 enables the persons in charge to advance the conveyor 2 through a considerable distance (corresponding substantially to that between the head 15 and the sealing structure 23) or through a series of short distances whose length is determined by that quantity of fluid which must be forced into the compartment 17a of the piston rod 17 in order to move the plunger 18 from engagement with the shoulder 20 into engagement with the second stop 28.

The valve 11 may be adjusted by hand or automatically. For example, the motor 7 can be equipped with a pressure gauge 50 which monitors the pressure in the annular chamber 24 and/or in the compartment 17a and adjusts the valve 11 (see the operative connection 51) in automatic response to rising fluid pressure in the chamber24 and/or compartment 17a when the plunger 18 engages the second stop 28. Such adjustment preferably involves automatic resetting of valve 11 to connect the hose 13 with the return conduit 10 and to seal the hose 12 from the supply conduit 9 so that the spring 19 is free to contract and returns the plunger 18 into engagement with the shoulder 20. It is clear that the spring 19 can be replaced by a spring (not shown) which reacts against the second stop 28 or head 30 and biases the plunger 18 rearwardly, i.e., toward the shoulder 20 or another suitable first stop. The placing of the spring into the compartment 17a behind the plunger 18 is preferred at this time because the spring does not interfere with removal and reinsertion of the second stop 28.

It is further clear that the second stop 28 can be replaced by other means for determining the foremost position of the plunger 18 in the compartment of the piston rod 17. For example, and as shown in FIG. 3, the head 30 may be provided with a projection 55 which extends into the compartment 17a and serves as an abutment for the plunger 18 (not shown). The projection 55 can be made rigid with the head 30 or it may be movable axially of the piston rod 17 and head 30. To this end, the projection 55 may constitute a feed screw whose external threads 56 mate with internal threads of the head 30, or the head 30 can be provided'wityh internal threads (shown at 30a) mating with external threads of the piston rod 17 so that the projection 55 can be moved toward or away from the shoulder 20 by rotating the head 30 relative to the piston rod 17. Still further, and as shown in FIG. 4 the projection 55 may constitute a pin or post which is provided with a set of diametrically extending bores 57 similar to the bores 27 and adapted to receive a bolt 58 or the like (similar to the abutment 28) which can be inserted into the head 30 to thereby fix the pin or post in a selected axial position. Thus, the second stop for the plunger 18 may be a fixed abutment whose position cannot be changed, an abutment which can be moved stepwise (e.g., by placing the abutment 28 into a different bore 27) or a projection which can be moved between an infinite number of different axial positions.

The motors 7 can be mounted in such a way that the heads 15 are connected with the conveyor 2 and the heads 30 are connected with the mobile mine roof supports 8, especially if the conveyor need not be advanced in a series of successive stages.

An important advantage of the improved hydraulic motors is that they can be installed in existing mining machines, that they occupy less room than heretofore known motors which are equipped with auxiliary aggregates, and that they are less expensive than conventional motors plus auxiliary aggregates. Moreover, the stroke selecting and limiting elements of the improved motors are concealed so that they are subjected to negligible wear and are not likely to be contaminated, even after long periods of use. Still further, the improved motors can be readily designed to allow for selection of strokes of any desired length as well as to permit their piston rods to complete full strokes of maximum length in a single operation.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features which fairly constitute essential characteristics of the generic and specific aspects of our contribution to the art and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims:

1. Apparatus for displacing heavy and bulky structures, particularly for pushing a material evacuating conveyor and material removing means toward the mine face in an underground excavation, comprising an anchor; a fluid-operated motor including a cylinder having a closed end, a piston reciprocable in and defining with said cylinder a first chamber adjacent to said closed end, a hollow piston rod connected to said piston and having an end extending from said cylinder in a direction away from said closed end, one of said ends being connected to .said anchor and said piston rod having a fluid-filled compartment and defining with said cylinder and with said piston a fluid-filled second chamber, means communicating said second chamber with said compartment, an axially movable plunger in said compartment, first and second stops provided in said piston rod to limit the extent of movement of said plunger, said first stop being engaged by said plunger when the latter is nearest to said piston, and biasing means for urging said plunger against said first stop; a source of pressurized fluid; and valve means actuatable in one-position to block fluid flow from said second chamber and to connect said source with said first chamber to thereby increase the distance between said closed end and said piston so that the other of said ends moves away from said anchor and the volumes of said first and second chambers respectively increase and decrease whereby the fluid flowing from said second chamber into said compartment moves said plunger from saif first against said second stop to thus terminate the admission of fluid into said first chamber, said valve means being further actuatable to a second position to permit the outflow of fluid from said second chamber and to thus permit said plunger to return into engagement with said first stop under the action of said biasing means while said first chamber remains sealed by said valve means, said piston being movable in said cylinder through a predetermined maximum distance exceeding that distance which said piston must cover to transfer from said second chamber into said compartment enough fluid to move said plunger from said first stop against said second stop so that said piston can cover said maximum distance in at least two stages the second of which takes place in response to renewed admission of fluid into said first chamber upon completed return movement of said plunger against said first stop.

2. Apparatus as defined in claim 1, wherein said anchor is a mobile mine roof support.

3. Apparatus as defined in claim 1, wherein at least one of said stops is adjustable in the longitudinal direction of said piston rod to thereby select the distance which said piston must cover relative to said cylinder or vice versa in order to effect the movement of said plunger from said first stop against said second stop.

4. Apparatus as defined in claim 3, wherein said one stop is said second stop.

5. Apparatus as defined in claim 1, further comprising first and second sealing means interposed between said piston and said cylinder and between said plunger and said piston rod.

6. Apparatus as defined in claim 1, wherein said communicating means includes at least one passage in said piston rod permitting the flow of fluid between said second chamber and said compartment in the region between said plunger and said piston.

7. Apparatus as defined in claim 1, wherein said fluid is a hydraulic fluidand further comprising means for collecting the fluid which is evacuated from said second chamber in response to movement of said plunger from said second stop against said first stop.

8. Apparatus as defined in claim 1, wherein said valve means comprises a multi-way distributor valve.

9. Apparatus as defined in claim 8, wherein said fluid is a hydraulic fluid and further comprising means for collecting the fluid which is discharged from said second chamber during movement of said plunger against said first stop.

10. Apparatus as defined in claim 9, further comprising means for adjusting said valve in response to completed movement of said plunger against said second stop so that said valve thereupon admits pressurized fluid into said first chamber.

11. Apparatus as defined in claim 10, wherein said adjusting means comprises means for monitoring the fluid pressure in said second chamber.

12. Apparatus as defined in claim 1, wherein said first stop is an internal shoulder provided in said piston rod.

13. Apparatus as defined in claim 1, wherein said bias'ing means comprises a helical spring which is connected to said piston and to said plunger and is arranged to pull said plunger against said first stop.

14. Apparatus as defined in claim 1, wherein said piston rod is provided with a plurality of transversely extending bores spaced apart in the axial direction of said piston rod, said second stop including an abutment received in one of said bores and extending into the path of movement of said plunger in a direction away from said piston.

15. Apparatus as defined in claim 1, wherein said second stop includes a projection provided at said end of said piston rod and extending into said compartment in a direction toward said piston.

16. Apparatus as defined in claim 15, wherein said piston rod comprises a head provided at' said end thereof and supporting said projection.

17. Apparatus as defined in claim 15, wherein said projection is shiftable axially of said piston rod to thereby select the distance which said plunger covers during movement between saidstops.

18. Apparatus as defined in claim 17, wherein said projection is adjustable stepwise.

19. Apparatus as defined in claim 17, wherein said projection is adjustable between an infinite number of positions.

20. Apparatus as defined in claim 1, wherein said fluid is a hydraulic fluid and said source comprises a 21. Apparatus as defined in claim 1, wherein said valve means is actuatable in a third position to admit pressurized fluid into said first chamber while simultaneously permitting the outflow of fluid from said second chamberso that said piston can travel through said maximum distance in a single stroke 

1. Apparatus for displacing heavy and bulky structures, particularly for pushing a material evacuating conveyor and material removing means toward the mine face in an underground excavation, comprising an anchor; a fluid-operated motor including a cylinder having a closed end, a piston reciprocable in and defining with said cylinder a first chamber adjacent to said closed end, a hollow piston rod connected to said piston and having an end extending from said cylinder in a direction away from said closed end, one of said ends being connected to said anchor and said piston rod having a fluid-filled compartment and defining with said cylinder and with said piston a fluid-filled second chamber, means communicating said second chamber with said compartment, an axially movable plunger in said compartment, first and second stops provided in said piston rod to limit the extent of movement of said plunger, said first stop being engaged by said plunger when the latter is nearest to said piston, and biasing means for urging said plunger against said first stop; a source of pressurized fluid; and valve means actuatable in one position to block fluid flow from said second chamber and to connect said source with said first chamber to thereby increase the distance between said closed end and said piston so that the other of said ends moves away from said anchor and the volumes of said first and second chambers respectively increase and decrease whereby the fluid flowing from said second chamber into said compartment moves said plunger from saif first against said second stop to thus terminate the admission of fluid into said first chamber, said valve means being further actuatable to a second position to permit the outflow of fluid from said second chamber and to thus permit said plunger To return into engagement with said first stop under the action of said biasing means while said first chamber remains sealed by said valve means, said piston being movable in said cylinder through a predetermined maximum distance exceeding that distance which said piston must cover to transfer from said second chamber into said compartment enough fluid to move said plunger from said first stop against said second stop so that said piston can cover said maximum distance in at least two stages the second of which takes place in response to renewed admission of fluid into said first chamber upon completed return movement of said plunger against said first stop.
 2. Apparatus as defined in claim 1, wherein said anchor is a mobile mine roof support.
 3. Apparatus as defined in claim 1, wherein at least one of said stops is adjustable in the longitudinal direction of said piston rod to thereby select the distance which said piston must cover relative to said cylinder or vice versa in order to effect the movement of said plunger from said first stop against said second stop.
 4. Apparatus as defined in claim 3, wherein said one stop is said second stop.
 5. Apparatus as defined in claim 1, further comprising first and second sealing means interposed between said piston and said cylinder and between said plunger and said piston rod.
 6. Apparatus as defined in claim 1, wherein said communicating means includes at least one passage in said piston rod permitting the flow of fluid between said second chamber and said compartment in the region between said plunger and said piston.
 7. Apparatus as defined in claim 1, wherein said fluid is a hydraulic fluid and further comprising means for collecting the fluid which is evacuated from said second chamber in response to movement of said plunger from said second stop against said first stop.
 8. Apparatus as defined in claim 1, wherein said valve means comprises a multi-way distributor valve.
 9. Apparatus as defined in claim 8, wherein said fluid is a hydraulic fluid and further comprising means for collecting the fluid which is discharged from said second chamber during movement of said plunger against said first stop.
 10. Apparatus as defined in claim 9, further comprising means for adjusting said valve in response to completed movement of said plunger against said second stop so that said valve thereupon admits pressurized fluid into said first chamber.
 11. Apparatus as defined in claim 10, wherein said adjusting means comprises means for monitoring the fluid pressure in said second chamber.
 12. Apparatus as defined in claim 1, wherein said first stop is an internal shoulder provided in said piston rod.
 13. Apparatus as defined in claim 1, wherein said biasing means comprises a helical spring which is connected to said piston and to said plunger and is arranged to pull said plunger against said first stop.
 14. Apparatus as defined in claim 1, wherein said piston rod is provided with a plurality of transversely extending bores spaced apart in the axial direction of said piston rod, said second stop including an abutment received in one of said bores and extending into the path of movement of said plunger in a direction away from said piston.
 15. Apparatus as defined in claim 1, wherein said second stop includes a projection provided at said end of said piston rod and extending into said compartment in a direction toward said piston.
 16. Apparatus as defined in claim 15, wherein said piston rod comprises a head provided at said end thereof and supporting said projection.
 17. Apparatus as defined in claim 15, wherein said projection is shiftable axially of said piston rod to thereby select the distance which said plunger covers during movement between said stops.
 18. Apparatus as defined in claim 17, wherein said projection is adjustable stepwise.
 19. Apparatus as defined in claim 17, wherein said projection is adjustable between an infinite number of Positions.
 20. Apparatus as defined in claim 1, wherein said fluid is a hydraulic fluid and said source comprises a supply conduit extending transversely of said cylinder in the region of said other end, and further comprising a return conduit arranged to receive fluid from said second chamber by way of said valve means during movement of said plunger toward said first stop, said return conduit being adjacent to said supply conduit and further comprising flexible conduits connecting said valve means with said first and second chambers.
 21. Apparatus as defined in claim 1, wherein said valve means is actuatable in a third position to admit pressurized fluid into said first chamber while simultaneously permitting the outflow of fluid from said second chamber so that said piston can travel through said maximum distance in a single stroke. 